“Living fossils” are unique, not ancient, say scientists

Graphical abstract. Credit: Systematic Biology (2023).

Researchers have introduced a new way to measure the uniqueness of species, challenging the idea that “living fossils” like the lungfish have stopped evolving.

This new metric, called “evolutionary heritage,” highlights unique traits that species develop over time, which is important for understanding and preserving biodiversity.

Scientists from Imperial College London, the Zoological Society of London, and the University of Canterbury in New Zealand have developed this metric to track how species traits accumulate and disappear through evolution.

Their findings, led by Professor James Rosindell from Imperial, were published in the journal Systematic Biology.

Traditionally, biodiversity was measured by counting species in an ecosystem. In the 1990s, scientists began focusing on evolutionary history, looking at how species are related.

Imagine a tree of life, where branches represent evolutionary lineages and leaves represent current species. By adding up the branches that connect different species to a common ancestor, scientists could measure evolutionary history.

However, this method doesn’t fully capture the unique functional traits that make species different.

For instance, Asian and African elephants are closely related but have distinct traits due to their different environments. African elephants have larger ears and more wrinkles to help them cool down.

Evolutionary heritage aims to capture all unique traits, even those not yet formally identified. It accounts for the accumulation and loss of traits over time. Species not only gain new traits but also lose some inherited from their ancestors.

This process can be modeled by algorithms that simulate the random chances of gaining or losing traits.

Dr. Will Pearse from Imperial College explains, “We’ve managed to mathematically capture something we’ve always cared about in evolutionary biology.” Professor Mike Steel from the University of Canterbury adds, “Evolutionary heritage handles the gain and loss of traits in a natural way.”

The new framework also offers insights into the concept of “living fossils.” Traditionally, living fossils are species that seem unchanged over long periods, resembling their ancient ancestors. However, many scientists argue this term is misleading, as it suggests evolution stops for these species, which is not true.

Professor Rosindell explains, “Evolution can’t be switched off. Organisms continue to mutate and evolve.” Evolutionary heritage identifies living fossils by the uniqueness and rarity of their traits rather than their resemblance to ancient species.

For example, some ancestral traits may survive in only a few modern species, while others are common. Species with rare ancestral traits are identified as living fossils using this method.

The team is now working on validating their ideas with genetic and trait data and developing their models for use in conservation and ecological research. This new approach helps better understand the complexity of evolution and the importance of preserving unique species traits.